Patients having impaired or no kidney function are normally treated by dialysis. Hemodialysis may take place e.g. during four hours each second day. During hemodialysis, the blood of the patient is circulated in an extra-corporeal circuit and passed through a dialysator having a semipermeable membrane, one side of which being in contact with the blood. The other side of the semipermeable membrane is in contact with a dialysis fluid having a certain composition. Waste products such as urea and creatinine may pass from the blood through the membrane to the dialysis fluid by means of diffusion driven by a concentration gradient. Other solutes, such as bicarbonate may pass the other way from the dialysis fluid through the membrane to the blood, e.g. to counteract acidification of the patient. Fluid is removed from the blood of the patient through the membrane. The dialysis fluid is normally discarded after the treatment. During a dialysis treatment of four hours, often several hundred liters of dialysate are used. Such a treatment normally takes place on a dialyse centre under the supervision of trained personnel.
Recently, dialysis machines have been produced intended for home use, wherein another person of safety reasons normally assists the patient. Online monitoring makes it possible to control or supervise the operation from a hospital. Such home-based dialysis can take place more often. The home dialysis treatment makes it possible to perform dialysis every day or even two times per day.
The drawback with conventional hemodialysis, as described above, is that the waste products accumulate between the treatments and the body is exposed to highly varying concentrations of e.g. urea and creatinine in the body fluids. Moreover, the patient cannot get rid of excess fluid between the treatments, which results in that the weight of the patient varies e.g. 4 kg between the treatments. In this case, 4 l of fluid may be removed from the patient during each treatment. This varying concentration of substances and load of fluid may be harmful for the patient and a more continuous hemodialysis treatment will be advantageous.
Thus, there is a need for a hemodialysis treatment, which may be performed continuously, which means that the dialysis system has to be portable so that the user can live a normal life.
Such a portable hemodialysis apparatus is shown e.g. in U.S. Pat. No. 4,269,708. The apparatus comprises a dialysator connected to the patient via conventional needles or catheters. The dialysator is also connected to a dialysis circuit having a vessel for clean dialysis liquid having a size of about 10 l. It is realised that this dialysis equipment is rather heavy but it is possible to carry it, e.g. as a backpacker. A smaller vessel may be connected for decreasing the weight temporarily. The device also comprises filters for removing toxic components such as an active carbon filter. Fluid is withdrawn from the blood in an ultrafiltration process and directly discarded to a receptacle. The apparatus according to U.S. Pat. No. 4,269,708 is, however, too heavy to be convenient to carry all the time. Thus, there is a need for a dialysis system, which is small and may be connected to the patient continuously. The system should be wearable and not too heavy.